Residual fuels



April 18, 1961 A. s.Ro :c|-m\1v|A ET Af. 2,979,890

RESIDUAL FUELS Filed Deo. l0, 195'? IN VEN TORS` HLBE R T G. ROCCH/N/ ByCHHRLES E. TRHUTHHN RESIDUAL FUELS ,'lhert G. Rocchini, Springdale,` andCharles E. Trautman, Cheswick, Pa., assignors to Gulf Research &

Development Company, Pittsburgh, Pa., a corporation of Delaware Y FiledDec. 1o, 1951, ser. No.f7o1,s47

s claims. (el. tio- 35.0

attacks such parts as boiler tubes, hangers, turbine blades,

and the like. These eiects are particularlynoticeable in gas turbines.`Large gas turbines show promise of becoming anl important type ofindustrial prime mover.

` However; economic considerations based on the efficiency of'. the gasturbine dictate the use of a fuelfor this purpose which is cheaper thana distillatediesel fuel; otherwise, other forms of poweri s uch asdiesel engines become competitive with gas turbines.` Y j One of themain problems arising in the use. of residual fuel oils in gas turbinesis thecorrosiveness inducedfby those residual fuels containingsufficient amounts 'of vanadium to cause'corrosion. Where no vanadium isvanadium, or none, asto present no corrosion problems, suchnon-corrosive fuelfoils are not always available at-the point where theoil is to be used. In such instance,- the cost of transportation of thenon-corrosive'oil, to the point of use lis often prohibitive, and theresidual oil loses its competitive advantage. These .factors appear tomilitate against the extensive useA of ,residual fuel oils for gasturbines. YAside from corrosion, the formation of d eposits upon theburning'of aresiduallfuel in a vgas turbine may result inunbalance ofthe turbine blades, .illog-v ging of openings and reduced thermalefficiency of the turbine.v

Substantially identical problems are encountered when u singa solidresidual' petroleum fuell containing substant1alaf-mounts of vanadium.These fuels are; petroleum residues obtained by known methods ofpetroleum relining such as deep Yvacuum reduction rof'asphalticfcrudesbottomspfollowed by distillation to'obtainsolidfresidues, coking ofliquid 4distillation bottoms, yand theplike. The solid residues thusobtained arevknownyar'iously as petroleum pitches or cokes andi fined:use as"v fuels. .Since present or the amount of vanadium is small, noappreci- 'able corroslon is encountered.:4 While many residual fuel voilsas normallyobtained in the refinery contain so littlethe-vanadiumcontent of the original crude oil tendsQto,

rcfincentrate"in the v'residual fractions, and since'jrthe'processing'4of. the fresidualj fractions to solid residues results in.furthericoncentration of the vanadium in theslid f residues, thevanadium corrosion problem tends to be in-Y tensiied in using the solidresidues asfu'el.

. 2,979,890 Patented Apr. 18, 1961 ICC of a residual fuel oil containingvanadium compounds,.

vigorously attack various metals, their alloys, and other materials atthe elevated temperatures encountered in the combustion gases, the `rateof attackvbecoming progres'- sively more severe as the temperature isincreased. The vanadium-containing ash forms deposits on the partsaffected and corrosively reacts with them. It is a hard,adherent'material when cooled to Yordinary temperatures. It hasnowbeendiscovered that residual petroleum fuels containing vanadium inan amount s'uicient to yield a corrosive vanadium-containing ash uponcombustion can berendered substantially less corrosivenotwithstand 'ingthe Vnormally corrosive vanadium content, by incorporating thereintoform a uniform blend a small amount, sufficient to retard thecorrosiveness of thel ash, of an alkali metal tungstate;v In the fuelcompositions of the invention, corrosiony due to the vanadium-containingash is substantially retarded. Y

In the. accompanying drawing, the single figure shows an apparatus fortestingvthe corrosivity of residual fueloil compositions.V Y Y .The typeof residual fuel oils to which the'inventionis directed is exemplifiedby No. 5, No.6 and Bunker C fuel 'oils which contain a ysufficientamount of vanadium to form a corrosive ash upon combustion. These areresidual type fuel oils obtained from petroleum by methods knownlto theartiv Forexample, residual fuel oils -late fuel oil Estocks, known ascutter stocks, and the invention also includes a residualY fuel koils soobtained,

provided that such oilscontain lsufficientvanadium normallyfvto exhibitthe corrosioncharacteristics described herein;I 'It-shouldbeunderstoodlthat distillate fuel oils themselves contain either novanadium or such small amounts as 'to present no problem ofjcorrosion.The total ash from commercial-residual. fuel oils usually rangesfromabout 0,02 to `0.2 percent :by weight-The vanadium pentoxide (V205)content of such'ashes ranges from zero to vtrace amounts up to about 5percent by weightV for low vanadium stocks, exhibiting no significantvanadiumcorrosion problem, vto as much as percent byweight for some ofthe 4high Avanadium stocks','.exhibit} ing severe corrosion. Y v I n n.i.

The Ytype 0f vanadium-containing solid residual fuelsfto' which-,theinvention is directed'is exemplified by the coke Y i obtained inknownmanner by the'delayedthermal coking or' fluidized coking of toppedor reduced crude oils and to obtain solid residues, visbreaking of`liquid distillation byd'thexpltches Obtamed m known manner by' the deepvacuum-reduction ofiasphaltic crudesto 'obtain solidv residues. Thesematerials have ashA contents Vofthe order of 0.18 percent by weight,more or less,;and contain corrosive amounts of vanadium whenpreparedfrom stocks containing substantialamounts of vanadium.' A:typical pitchvexhibiting corrosive characteristics .uponY combustion.had a softening point of 347-F. and a vanadium content, as vanadium, of578 parts per million;

They corrosion retarding additive of the invention is,v

`as has been stated, an alkali metal tungstate. The addi-Y@The'vanadium-containing\ash present inthe'hot flue gasiobtainedfromthe burning of a residual fuel containing' substantial amounts ofvanadium compoundscauses tema Onh sorrosion 9i thewrbinablades andtothertive is employed in thedryform or as a water solution.-

The alkaliV metal tungstates include the sodium,l potas-I sium, lithium,rubidium and cesium tungstates in any of n the ortl1 ometa`orpara-tungstate formsLBecauseof' 3 their availability and relatively lowcost, the sodium Iand potassium tungstates are preferred.

When employing in residual fuels the dry alkali metal tungstates, it isdesirable to use the finely-divided salts. However,- `the degree towhich the salts are subdivided is not critical. One requirement forusing a tinelydivided material is based upon the desirability of forminga fairly stable dispersion or suspension of the salts when blended witha residual fuel oil. Furthermore, the more finely-ydivided materials aremore eicient in forming uniform blends and rendering non-corrosive therelatively small amounts of vanadium in a residual fuel, whether thefuel be solid or liquid. Thedry salts are ,therefore employed `in aparticle size range of less than 250 microns, prefer.- ably less than`50 microns. However, since the alkali metal tungstatesA are soluble inwater, it is unnecessary to employ the finely dvided'dry additives whenit is desired to employ water solutions thereof. Thus, the salts can bedissolved in water to form more or less concentrated solutions and thesolutions then are emulsied in the fuel.

In the practice of the invention with vanadium-containing residual fueloils, the additive is uniformly blended with the oil in proportion tothe vanadium content thereof. This is accomplished by suspending thenelydivided dry salts in the oil, as has been indicated above,

emesso i or by emulsifying oridispersing a water solution of the V saltsin the oil. If desired, suitable surface active agents, Such as sorbitanmonooleate and monolaurate and the ethylene oxide condensation productsthereof, glycerol monooleate, and the like, which promote thesuitability of the suspensions or emulsions can beV employed.

In the practice of the invention with the solid residual fuels,incorporation of the 'additive of the invention is accomplished inseveral ways. The additive can be suspended or emulsiedin the liquidvanadium-containing residual stocks or crude oil stocks from which thesolid residual fuels of the invention are derived, and the mixture canthen be subjected to the refining process which Willproduce thesolid'fnel. For example, in the production of a pitch by the deep vacuumreduction of an asphaltic crude'oil, sodium ortho tungstate or asolution thereof in water isslurried with the oil in' proportionto thevanadium content thereof, and the whole subjected to deep vacuumreduction to obtain a pitch containing the additive uniformly dispersedtherein. As stll another alternative; particularly with a pitch which'iswithdrawnl inmolten form from the processing vessel, the additive canbemixed with the molten pitch and the mixture al lowed to solidfy afterwhich it is ground to the-desired size... Y

In the case of either liquid or solid residual fuels, the additive vcanbe separately fed into the burner as the dry`,salts, an oil dispersionthereof or a water solution thereof. In any such case, it is preferred'to meter the additive into the fuel line just. prior to` the combustionzone. Inagasfturbine plant where the heat resisting metallic parts'areexposed to hot combustion gases at temperatures of the'order of 1200 F.and above, the additive can be `added separately from the fuel eitherprior to or during combustion itself, or even subsequent to combustion.VHowever, it may specifically be added, whether in admixture with orseparately from the fuel, theA additive `is introduced into said plantupstream of the heat resisting metal parts to be' protected fromcorrosion. y

The alkali metal tung'states` are employed In'a small amount withrespectto the vanadium-containing residual fuel, sucient to retard thecorrosiveness ofthe ash. Although the exact amount of additive to usenwill vary in accordance with the vanadium content ofthe specific re-usidual fuel employed, Yas will be understodby those 4 skilled inthe art,in general a reduction'in corrosivity is already observed with anamountmf the alkali metal tungstate sufficient to yield about 1 atomweight of the tungsten present in the additive per atom weight ofvanadium in the residual fuel. However, corrosivity is minimized when anamount of additive is employed yielding from about 3 to about 6 atomweights of tung sten per atom weight of Vanadium in the residual fuel,and appears to be `at a minimum at an atom weight ratio of tungsten tovanadium of 3: 1.

The following specific examples are further illustrative of theinvention.

A, series of residual fuel oil compositions employing varying amounts ofadditive are made up and tested under conditions of burning residualfuel oils in a gas turbine. Identical tests are run on the residual fueloil containing no additive. In the testing the apparatus shown in thedrawing is employed. As shown therein, the residual oil under test isintroduced through line 10 into a heating coil 11 disposed in a tank ofwater 12 maintained .at such temperature that the incoming fuel ispreheated to a temperature of approximately 212 F. From the heating coil11 the preheated oil is passed into an atomizing head designatedgenerally as 13. The preheated oil passes through a passageway 14 into anozzle 15 which consists `of a #26 hypodermic needle of approximately0.008 inch I D. and 0.018 inch O.D. The tip'of the nozzle is groundsquare and allowed to project slightly through an orifice 16 ofapproximately 0.020 inch diameter. The orifice is supplied with 65p.s.i.g. air for atomization of the fuel, into the combustionchamber,21. ,The air is introduced through line 17, preheat coil 18in'tank 12, and air passageways 19 and 20 in the atomizing head 13. Thecombustion chamber 21 is made up of two concentric cylinders 22 and 23,respec4 tively, welded to` two end plates 24 and 25. Cylinder 22 has adiameter of 2 inches and cylinder 23 has a dif ameter of 3 inches; thelength of the cylinders between the end plates is 81/2 inches. End plate24 has a central opening 26 into which the atomizing head is inserted.End plate 25 has a one (1) inch yopening 27 covered by a baffle plate 28mounted in front of it to prevent direct blast of ame on the testspecimen 29. Opening 27 in end plate 125 discharges `into a smallercylinder 30 havf ing a diameter of 11/2 inches and a length of 6 inches.The .specimen 29 is mounted near the downstream end of thecylinderapproximately 1% inches from the outlet thereof. Combustion air isintroduced by means of air inlet 31into the annulus between cylinders 22and 23, thereby preheating the combustion air, and then through threepairs of 3/16 inch tangential air inlets 32 in the inner cylinder 2,2.The-first pair of airinlets is spaced 1A. inch from end plate 24; thesecond pair 3%: inch from the first; and the third` 3 inches from thesecond. The additionaly heating required to bring the combustionproducts to test temperature is supplied by an electric heating coil 33surrounding the outer cylinder 23. The entire combustion assembly issurrounded bysuitableinsulation 34. The test specimen 29 is a metal discone inch in diameter by 0.125,V inch thick, (with a hole` in the centerby means'of, which the specimen is attached to a tube 3Scontaining,thermocouples. The specimen and tube assembly are mounted ona suitable stand' 36.

In conductinga test in the above-described apparatus, a weighed metalspecimen is ,exposed tothe combustion productsofja residual fuel oil,the specimen being maintainedl at a selected Atest temperaturev of, forexample,- l350, 14S0'or 71550 F. by the heat of the combustion products.The test isusually` run for ,a period of hours with the rate of fuelfeed being l/2 pounclper hour Aand the'rate of atomizing air feed being2V pounds per hour. The combustion airl entering through air inlett31 isfed at 25 pounds per hour. At the end of the test run the specimeniisreweighed to determine the weightiof deposits and is tliendescaled witha conventional alka line descialin'g salt in molten condition at 4750,oC. Afterdescaling, the specimen is'dipped in 67N hydrochloric acidcontaining a conventional pickling inhibitor, and is then washed, driedand weighed. The loss in weight of the specimen after descaling is thecorrosion loss.

The compounded and uncompounded residual fuel oils are tested in theapparatus just described using a 25-20 stainless steel as the testspecimen. The tests are run for 100 hours at a temperature of 1450 F.under the conditions described above. ployed as a base fuel has thefollowing inspection:

Gravity, A.P.I. 20.6 Viscosity, Furol, Sec.:

122 F. 25.4 Flash, OC: F. 255 Fire, OC: F. 295 Sulfur, B: percent 1.6Ash: percent 0.04 Vanadium: p.p.m. of oil 182 Sodium: p.p.m. of oil 2The alkali metal tungstate employed in this series of runs is sodiumpara tungstate (Na6W7O24-l6H2O).

The following table shows the make-up and the reduction in corrosion anddeposits obtained in the tests.

TABLE I Fuel Ex. 1 Ex. 2 Ex. 3 Ex. 4 (Blank) Amount of Additive:

Percent by Wt. of Fuel.- 0. 15 0. 2 0.3 0. 7 Atom Ratio, W:V 0 1.5:1 2:13:1 ,6:1 Corrosion, Wt. Loss of Specimen, Mg./Sq. In 1, 580 128 97 7 28Reduction in Corrosion Due to Additive, Percent 92 94 99. 5 99 Depositson Specimen, Mg./

Sq. 1, 130 276 115 119 164 Texture of Deposits Hard Hard Pow- Pow- Pow-Scale Dalat dery dery dery pos It is apparent from the 'foregoing datathat sodium tungstate is an eificient corrosion inhibitor and is mosteffective when employed in an amount yielding an atom Weight ratio, W:V,of 3:1. Similar results are obtained employing the other alkali metaltungstates disclosed herein.

The following example is illustrative of the use of the additive of theinvention with solid residual fuels.

Example 5 Melt a solid petroleum pitch obtained from the deep vacuumreduction of an asphaltic crude. This pitch has a softening point of 347F. and a vanadium content of 578 parts per million. While the pitch isin molten form, add and uniformly blend therein with stirring 1.25percent by weight of finely powdered dry potassium ortho tungstate(K2WO4-2H2O). Upon cooling and solidfica- The residual oil emf tion,grind the mixture to about mesh. The result ing fuel has an atom weightratio, W:V, of 3:1.

A typical analysis of the 25-20 stainless steel employed in the testingdescribed is shown in the following table in percent by weight.`

Resort may be had to such modifications and variations as fall withinthe spirit of the invention and thescope of the appended claims.

We claim:

1. A fuel composition comprising a uniform blend of a residual petroleumfuel yielding a corrosive vanadiumcontaining ash upon combustion and anamount of an alkali metal tungstae suiiicient to yield from about 3 toyabout 6'atom weights of tungsten per atom weight of vanadium in saidfuel. l

2. The fuel composition of claim 1, wherein the fuel is a solid residualfuel.

3. A fuel composition comprising a uniform blend of a residual petroleumfuel oil yielding a corrosive vanadium-containing ash upon combustionand an amount of a sodium tungstate su'icient to yield from about 3 toabout 6 atom weights of tungsten per atom weight of vanadium in saidfuel oil.

4. The fuel composition of claim 3, wherein the tungstate is sodiumparatungstate.

5. In a gas turbine plant in which a fuel oil containing vanadium isburned and which includes heat resistant metallic parts exposed to hotcombustion gases and liable to be corroded by the corrosivevanadium-containing ash resulting from the combustion of said oil, themethod of reducing said corrosion which comprises introducing into lsaid plant upstream of saidparts an amount of an alkali metal tungstatesufcient to yield from about 3 to about 6 atom weights of tungsten peratom weight of vanadium in said fuel oil.

References Cited in the le of this patent FOREIGN PATENTS

5. IN A GAS TURBINE PLANT IN WHICH A FUEL OIL CONTAINING VANADIUM ISBURNED AND WHICH INCLUDES HEAT RESISTANT METALLIC PARTS EXPOSED TO HOTCOMBUSTION GASES AND LIABLE TO BE CORRODED BY THE CORROSIVEVANADIUM-CONTAINING ASH RESULTING FROM THE COMBUSTION OF SAID OIL, THEMETHOD OF REDUCING SAID CORROSION WHICH COMPRISES INTRODUCING INTO SAIDPLANT UPSTREAM OF SAID PARTS AN AMOUNT OF AN ALKALI METAL TUNGSTATESUFFICIENT TO YIELD FROM ABOUT 3 TO ABOUT 6 ATOM WEIGHTS OF TUNGSTEN PERATOM WEIGHT OF VANADIUM IN SAID FUEL OIL.